Justin Collins
1/7/2009 10:28:00 AM
Zhao Yi wrote:
> I use this method to run an external program:
>
> output=`uname -r | sed 's/\([^\.]*\.[^\.]*\)\.*.*/\1/'`
> puts output
>
> ruby will ignore the sed command. Doesn't ruby support "|"?
>
The sed command is not being ignored. The issue is that the backticks
(`) do string interpolation before sending the command, which means your
backslashes are removed before the commands are sent to the shell.
Take a look at this:
irb(main):001:0> puts `uname -r | sed 's/\([^\.]*\.[^\.]*\)\.*.*/\1/' &&
ps x | grep uname`
2.6.27.5-desktop-2mnb
24178 pts/8 S+ 0:00 sh -c uname -r | sed 's/([^.]*.[^.]*).*.*/?/'
&& ps x | grep uname
24182 pts/8 S+ 0:00 grep uname
=> nil
irb(main):002:0> puts system 'uname -r | sed
"s/\([^\.]*\.[^\.]*\)\.*.*/\1/" && ps x | grep uname'
2.6
24187 pts/8 S+ 0:00 sh -c uname -r | sed
"s/\([^\.]*\.[^\.]*\)\.*.*/\1/" && ps x | grep uname
24191 pts/8 S+ 0:00 grep uname
true
=> nil
irb(main):003:0> puts `uname -r | sed
's/\\([^\\.]*\\.[^\\.]*\\)\\.*.*/\\1/' && ps x | grep uname`
2.6
24201 pts/8 S+ 0:00 sh -c uname -r | sed
's/\([^\.]*\.[^\.]*\)\.*.*/\1/' && ps x | grep uname
24205 pts/8 S+ 0:00 grep uname
=> nil
-Justin